1. Field of the Invention
This invention relates to a case for mounting electronic equipment that uses air cooling, and more specifically to a filter with a variable impedance for use in such a case.
2. Description of Related Art
In the electronic industry, the trend toward faster operating speeds and increased circuit density has created a trend towards ever-increasing power consumption. With this increase in power consumption comes a need for increased heat dissipation and component cooling.
Electronic equipment is typically cooled by forcing air over the equipment in order to carry away the dissipated heat. Referring to FIG. 1, air is flowed over equipment (not shown) mounted inside a case 100. Air movers 150 expel air from the top of the case and draw air in from the bottom. Because cases are often stacked close to each other vertically, plenums such as plenum 160, open to the front, rear, and/or side of the case 100, are used to insure proper spacing in order to intake and exhaust air. Air movers 150 are often mounted in the back of the case or inside a plenum 170 located at the top of the case.
Air enters plenum 160 horizontally and turns upwards before entering the section of the case where equipment is mounted. Several techniques are employed to assist in redirecting the air and to assist in evenly distributing the air flow after the air has made this turn. One technique used to evenly distribute the air is to use a lower baffle 130 that the air must first pass through to enter the case. Baffle 130 has holes drilled in it for air to flow through. By varying the hole size in one or both axes perpendicular to the airflow through the electronics to be cooled, the impedance to the air can be varied (section 120, pictured across the back of baffle 130, is shown with smaller holes than the front section of baffle 130).
In addition, ramps 110 may be used to further distribute the air evenly across the bottom of the case. Ramps 110 are placed in lower plenum 160 in order to re-direct the air from moving horizontally across the case to moving vertically into the case. Ramps of various heights can be used such that the air is redirected in a manner that evenly distributes the air front-to-back.
Air mover placement is also used to ensure air evenly exits the case. In the case top view of FIG. 2, more fans 150 are placed toward the front of the case to counter the air flow's tendency to exit towards the back of the case.
These techniques are not necessarily employed individually, but often times many if, not all, of them are employed simultaneously.